PUBLIC ABSTRACT Opioid use disorder (OUD) among pregnant women results in a number of adverse consequences in infants and mothers, including: preterm birth, low birth weight, birth defects, neonatal abstinence syndrome (NAS), and cog- nitive deficits in children. Pregnant women with OUD have elevated rates of HIV/HCV infection, psychiatric dis- orders, non-opioid substance use disorder (SUD); and social, financial, and employment problems. Pregnant women with OUD also have had sharp increases in treatment admissions in the last decade. Unfortunately, pregnant women with OUD also have high rates of treatment dropout. While medication assisted treatment com- bined with psychosocial services is the standard of care for opioid dependent pregnant women, it is not clear which psychosocial service is optimal. One promising intervention is patient navigation (PN), an evidence-based practice shown to be effective for a variety of psycho/social/emotional outcomes. PN has been shown to benefit problems common in those with OUD, including access to treatment, engagement in care, and motivation to improve health behaviors. The current study will build on our preliminary studies and further establish the internal and external validity of these findings and the potential value of the PN intervention. The first Specific Aim of this project will involve using Marlatt and Gordon?s relapse prevention model wherein we will infuse relapse preven- tion content for identification/prevention of (1) high risk situations of discontinuance of medication assisted treat- ment and (2) initial abstinence lapses. The second Specific Aim of this project will involve expanding our proof- of-concept study intervention and protocols to facilitate a multisite, randomized, system-wide trial; which will include uniform intervention, recruitment, randomization, study staff blinding, formalized follow up procedures, and staff training materials. The third Specific Aim of this project will involve implementing and testing the ex- panded intervention and protocols with pregnant women with OUD (n=122) at two hospital sites, Magee-Wom- ens Hospital of UPMC and the University of Utah Hospital. Participants will be randomized to PN or standard care and will be assessed at baseline, prior to delivery, and 2 and 6 months postnatal. Completion of this project will result in necessary protocols/procedures and pilot data preparatory to a large scale, fully powered, multisite randomized trial. This work addresses a major public health issue, opioid dependence during pregnancy, and further establishes an evidence base for protecting health of mother and baby.